Texas Instruments TIDA-060040, Manual

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Of all the alignment cases, on-axis is the most forgiving of mechanical alignment errors. Overall the field vector
remains nearly parallel to the face of the magnet and therefore magnitude and phase shifts at the input are not
as significant as is seen with the other alignment cases.
Table 3-2. On-Axis Harmonic Correction Factors
HARMONIC α
i
β
i
1 0.42 –0.73
2 –0.35 0.07
3 –0.01 0.06
4 –0.02 0.01
On-Axis Calibrated Angle Error shows the resulting error for both a direct arctangent calculation and for the
CORDIC output after applying the harmonic data.
Angle (deg)
A
ngle E
rror (d
eg)
0 45 90 135 180 225 270 315 360
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Calibrated Atan Error
Calibrated CORDIC Error
Figure 3-12. On-Axis Calibrated Angle Error
It is worth noting here that the 0.25° resolution of the TMAG5170 CORDIC output does limit the measurement
accuracy. To achieve the highest accuracy, directly calculate the arctangent result from the X and Y component
outputs of the device. The benefit of the CORDIC output of TMAG5170 is that it reduces the burden for the
microprocessor and can reduce overall measurement latency.
3.3.3 TMAG5170 In-Plane
The in-plane alignment differs from the on-axis approach in that the sensor is placed coplanar to the magnet.
This produces the smallest profile solution overall, but produces highly imbalanced input magnitudes.
Additionally, this alignment is the most susceptible to mechanical errors which is evident when examining
the peak angle error. This position is very sensitive to eccentricity errors in the magnet rotation. Any magnet
centering misalignment results with a changing airgap range. As demonstrated in
In-Plane Magnitude vs Airgap
Distance , small variations at this range have a significant impact on the magnitude of the magnetic field. It is
particularly important when configuring a sensor in this position to exercise a great deal of care to achieve an
exact mount for the magnet.
Additionally, at the outer edge of the magnet, the field vector direction is constantly changing as it wraps around
to the opposing magnet pole. As a result tilt and alignment errors will result in phase error and changing input
amplitudes.
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